Adsorption of glycosaminoglycans onto hydroxyapatite using chromatography

Sustained local ionic homeostatic imbalance caused by calcification modulates inflammation to trigger heterotopic ossification

Heterotopic ossification (HO) is a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues. Despite being a frequent complication of orthopedic and trauma surgery, brain and spinal injury, the etiology of HO is poorly understood. The aim of this study is to evaluate the hypothesis that a sustained local ionic homeostatic imbalance (SLIHI) created by mineral formation during tissue calcification modulates inflammation to trigger HO. This evaluation also considers the role SLIHI could play for the design of cell-free, drug-free osteoinductive bone graft substitutes. The evaluation contains five main sections. The first section defines relevant concepts in the context of HO and provides a summary of proposed causes of HO. The second section starts with a detailed analysis of the occurrence and involvement of calcification in HO. It is followed by an explanation of the causes of calcification and its consequences. This allows to speculate on the potential chemical modulators of inflammation and triggers of HO. The end of this second section is devoted to in vitro mineralization tests used to predict the ectopic potential of materials. The third section reviews the biological cascade of events occurring during pathological and material-induced HO, and attempts to propose a quantitative timeline of HO formation. The fourth section looks at potential ways to control HO formation, either acting on SLIHI or on inflammation. Chemical, physical, and drug-based approaches are considered. Finally, the evaluation finishes with a critical assessment of the definition of osteoinduction. STATEMENT OF SIGNIFICANCE: The ability to regenerate bone in a spatially controlled and reproducible manner is an essential prerequisite for the treatment of large bone defects. As such, understanding the mechanism leading to heterotopic ossification (HO), a condition triggered by an injury leading to the formation of mature lamellar bone in extraskeletal soft tissues, would be very useful. Unfortunately, the mechanism(s) behind HO is(are) poorly understood. The present study reviews the literature on HO and based on it, proposes that HO can be caused by a combination of inflammation and calcification. This mechanism helps to better understand current strategies to prevent and treat HO. It also shows new opportunities to improve the treatment of bone defects in orthopedic and dental procedures.

The effect of water on the binding of glycosaminoglycan saccharides to hydroxyapatite surfaces: a molecular dynamics study

Classical molecular dynamics (MD) simulations have been employed to study the interaction of the saccharides glucuronic acid (GlcA) and N-acetylgalactosamine (GalNAc) with the (0001) and (011̄0) surfaces of the mineral hydroxyapatite (HAP). GlcA and GalNAc are the two constituent monosaccharides of the glycosaminoglycan chondroitin sulfate, which is commonly found in bone and cartilage and has been implicated in the modulation of the hydroxyapatite biomineralization process. MD simulations of the mineral surfaces and the saccharides in the presence of solvent water allowed the calculation of the adsorption energies of the saccharides on the HAP surfaces. The calculations show that GalNAc interacts with HAP principally through the sulfate and the carbonyl of acetyl amine groups, whereas the GlcA interacts primarily through the carboxylate functional groups. The mode and strength of the interaction depends on the orientation of the saccharide with respect to the surface and the level of disruption of the layer of water competing with the saccharide for adsorption sites on the HAP surface, suggesting that chondroitin 4-sulfate binds to the layer of solvent water rather than to HAP.

Dentin adhesion and MMPs: a comprehensive review

This review examines the fundamental processes responsible for the aging mechanisms involved in the degradation of resin-bonded interfaces, as well as some potential approaches to prevent and counteract this degradation. Current research in several research centers aims at increasing the resin-dentin bond durability. The hydrophilic and acidic characteristics of current dentin adhesives have made hybrid layers highly prone to water sorption. This, in turn, causes polymer degradation and results in decreased resin-dentin bond strength over time. These unstable polymers inside the hybrid layer may result in denuded collagen fibers, which become vulnerable to mechanical and hydrolytical fatigue, as well as degradation by host-derived proteases with collagenolytic activity. These enzymes, such as matrix metalloproteinases and cysteine cathepsins, have a crucial role in the degradation of type I collagen, the organic component of the hybrid layer. This review will also describe several methods that have been recently advocated to silent the activity of these endogenous proteases.

Binding of glycosaminoglycan saccharides to hydroxyapatite surfaces: A density functional theory study

Density functional theory calculations implemented by the SIESTA code are used to study the interactions of the saccharides N-acetylgalactosamine (GalNAc) and glucuronic acid (GlcA) with the (0001) and [Formula: see text] surfaces of the mineral hydroxyapatite (HAP). GalNAc and GlcA are the constituent monosaccharides of chondroitin, which is a glycosaminoglycan found in bone and cartilage, and whose interactions with HAP have been implicated as a controlling factor in the process of biomineralisation. Geometry optimisation calculations are used to identify low energy adsorption structures of the monosaccharides on the HAP surfaces, and to calculate the corresponding adsorption energies. The calculations show that GalNAc interacts with HAP principally through its hydroxy and acetyl amine functional groups, and deprotonated GlcA interacts principally through its hydroxy and carboxylate functional groups. The mode and strength of adsorption depends on the orientation of the saccharide with respect to the HAP surface, which has implications for the structural conformation of chondroitin chains in the presence of hydroxyapatite. Both monosaccharides bind more strongly to the [Formula: see text] surface than to the (0001) surface.

Adhesion to chondroitinase ABC treated dentin

Dentin bonding relies on complete resin impregnation throughout the demineralised hydrophilic collagen mesh. Chondroitin sulphate-glycosaminoglycans are claimed to regulate the three-dimensional arrangement of the dentin organic matrix and its hydrophilicity. The aim of this study was to investigate bond strength of two etch-and-rinse adhesives to chondroitinase ABC treated dentin. Human extracted molars were treated with chondroitinase ABC and a double labeling immunohistochemical technique was applied to reveal type I collagen and chondroitin 4/6 sulphate distribution under field emission in-lens scanning electron microscope. The immunohistochemical technique confirmed the effective removal of chondroitin 4/6 sulphate after the enzymatic treatment. Dentin surfaces exposed to chondroitinase ABC and untreated specimens prepared on untreated acid-etched dentin were bonded with Adper Scotchbond Multi-Purpose or Prime and Bond NT. Bonded specimens were submitted to microtensile testing and nanoleakage interfacial analysis under transmission electron microscope. Increased mean values of microtensile bond strength and reduced nanoleakage expression were found for both adhesives after chondroitinase ABC treatment of the dentin surface. Adper Scotchbond Multi-Purpose increased its bond strength about 28%, while bonding made with Prime and Bond NT almost doubled (92% increase) compared to untreated specimens. This study supports the hypothesis that adhesion can be enhanced by removal of chondroitin 4/6 sulphate and dermatan sulphate, probably due to a reduced amount of water content and enlarged interfibrillar spaces. Further studies should validate this hypothesis investigating the stability of chondroitin 4/6 and dermatan sulphate-depleted dentin bonded interface over time.

Cell-compatible properties of calcium carbonates and hydroxyapatite deposited on ultrathin poly(vinyl alcohol)-coated polyethylene films

Poly(vinyl alcohol) (PVA) was coated onto polyethylene (PE) films by a repetitive adsorption and drying process, and then the PVA-coated PE films were alternately immersed into aqueous solutions of Ca2+ and CO3(2-) ions (alternate soaking cycles), to deposit calcium carbonate (CaCO3) onto the films. The PVA coating was essential for the CaCO3 deposition. The amount of CaCO3 deposited increased with an increasing number of cycles. Scanning electron microscopic observations and attenuated total reflection spectra revealed the presence of both calcite and aragonite as the crystal structures of CaCO3 on the film. L929 fibroblast cells adhered and proliferated on these CaCO3-deposited PE films, as well as the hydroxyapatite-coated PE films previously prepared. It was found that the PVA coating and the subsequent deposition of calcium salts on certain films facilitated cell compatibility.

Immunocytochemical analysis of dentin: A double-labeling technique

Immunocytochemical analysis is a fundamental and selective technique for identifying different molecular components of human dental structure. The hypothesis tested here is that the application of different etching solutions on dentin does not hinder collagen fibrils and proteoglycans from maintaining their immunochemical antigenicity. Human dentin disks were treated with 0.5M of EDTA, citric acid, maleic acid, or phosphoric acid (for 15 or 30 s). A double-immunolabeling technique was performed to identify, simultaneously, collagen fibrils and chondroitin sulfate. The use of different acids resulted in different degrees of labeling. Maleic and citric acids revealed a diffuse and intense labeling for both collagen fibrils and proteoglycans. The use of phosphoric acid on dentin showed a massive coagulation of the proteoglycans (15 s) or very low labeling (30 s). These data clarify that the use of acids on dentin components is able to modify their antigenicity. Moreover, the double-labeling immunocytochemical technique allows understanding of the spatial relationships between the collagen fibrils and proteoglycans of the dentin matrix.

Hydroxyapatite deposition by alternating soaking technique on poly(vinyl alcohol)-coated polyethylene films

A poly(vinyl alcohol) (PVA)-coating on polyethylene films, prepared by repetitive adsorption/drying in an aqueous PVA solution, accelerated hydroxyapatite (HAp) deposition by an altemate soaking in aqueous solutions containing Ca2+ and PO4(3-) ions. X-ray photoelectron spectra of the surface of the HAp-deposited film showed the presence of calcium and phosphorus of a suitable peak ratio for HAp formation. X-ray diffraction analyses also revealed peaks corresponding to HAp. Scanning electron microscopic observation showed the surface of the HAp layer to be smooth, with nano-ordered dotted threads in networks. A simple PVA coating on a surface will serve as a novel system for accelerated HAp formation via alternating soaking.

Dentin proteoglycans: an immunocytochemical FEISEM study

Dentin proteoglycans are fundamental constituents of the dentin matrix and are distributed ubiquitously both in dentin and cement. They have several important functional properties; in particular, they have a fundamental role in the maintenance and the correct stabilization of collagen fibers. The use of phosphoric acid on dentin, as proposed in most common dental adhesive systems to establish a reliable bond, may affect the molecular structure of proteoglycans. The aim of this study was to evaluate, after the application of EDTA or phosphoric acid on dentin, the dentin proteoglycans with an immunocytochemical approach with high resolution SEM. For this purpose, dentin disks obtained from recently extracted human molars were etched with a 35% water solution of phosphoric acid for 15 s, 30 s, and 60 s. Control specimens were conditioned with EDTA. Specimens were immunolabeled with a monoclonal antibody antichondroitin sulfate and visualized with a gold-conjugated secondary antibody. Conditioning dentin with EDTA resulted in a distinct labeling of the proteoglycans, as visualized on branching fibrillar structures in the order of 10-20 nm. The use of 35% phosphoric acid on dentin revealed a coagulation of proteoglycans after etching for 15 s while a very low labeling signal was detectable after 30 s. No labeling was obtained after etching dentin with phosphoric acid for 60 s. These results suggest that the use of 35% phosphoric acid on dentin is able to produce significant structural modifications of the dentin proteoglycans even after short application times. Additionally, when applied on the dentin surface for more than 30 s, phosphoric acid produces a dramatic decrease in proteoglycans' antigenicity, probably due to structural modifications of the three-dimensional conformation of these molecules.

Influence of charge density, sulfate group position and molecular mass on adsorption of chondroitin sulfate onto coral

The adsorption of chondroitin sulfate onto granules of natural coral of specific diameter, between 100 and 500 microm, having high calcium content (> 98%) and a homogeneous surface was investigated. Several chondroitin sulfate samples desulfated to various extents, with a sulfate to disaccharide ratio (charge density) of 0.98-0.07 and non-sulfated polysaccharide possessing a chondroitin sulfate backbone structure were tested for their ability to adsorb onto coral. Adsorption of chondroitin sulfate onto coral depends on its charge density, as the removal of sulfate groups totally abolishes this capacity. Various chondroitin sulfates of molecular mass from 26,950 to 1140 were also tested. No appreciable effect depending on the molecular mass was evident. Also, chondroitin sulfate fractions with molecular mass of about 3530 (formed by about 6 disaccharide units) and 1140 (formed by about 2 disaccharide units) retain their full capacity to adsorb onto coral. Furthermore, the position of sulfate groups inside the polysaccharide chains does not influence the ability of chondroitin sulfate to adsorb onto coral. In fact, chondroitin sulfate derivatives almost completely sulfated (> 90%) in position 4 of galactosamine and chondroitin almost completely (> 90%) sulfated in position 6 show a full adsorbtion onto coral. Thus, large amounts of chondroitin sulfate are adsorbed onto coral, and sulfate groups are of paramount importance in the adsorption process. On the other hand, the capacity of chondroitin sulfate to adsorb onto coral is quite aspecific. In fact, it does not depend on the presence of sulfate groups esterified in a specific position or sulfated sequences arranged in blocks but rather on the presence of sulfate groups, and this ability increases with increasing charge density, as indicated by the values of the Langmuir constant, the adsorption capacity, that decreases with decreasing chondroitin sulfate charge density reaching very low values for the totally desulfated polymer.

The interaction of recombinant decorin with alpha2HS-glycoprotein-implications for structural and functional investigations

Isolated protein preparations of the small leucine-rich proteoglycans (SLRPs) associated with mineralized tissues have provided important information in understanding their structural and functional interactions within extracellular matrices and their potential roles in mineralization. Two important SLRPs, decorin and biglycan, copurify following extraction and purification from mineralized tissues using standard procedures, and to overcome this problem decorin was synthesized within a mammalian expression system to obtain pure preparations. The expressed protein was purified from the culture medium using anion-exchange chromatography, and characterization confirmed the presence of a decorin-rich fraction. However, N-terminal sequencing revealed the additional presence of alpha2HS-glycoprotein (alpha2HSG), representing approximately 35% of the total purified fraction. The decorin-rich fraction was subjected to selected further purification techniques to separate decorin from alpha2HSG. Application of the sample at a low concentration (1 mg/ml) to a second anion-exchange procedure and elution over an expanded sodium chloride gradient resulted in a high degree of purity (98%), with a single protein isolate demonstrable by SDS-PAGE. Electroelution achieved partial purification ( approximately 89%), but immunoprecipitation with antibodies against the glycosaminoglycan chain and the polyhistidine tag failed to separate the two proteins. This study suggests there is a strong interaction between recombinantly produced decorin and alpha2 HSG and highlights the importance of the purification technique to the application of recombinantly produced proteins or those that have been extracted from mineralized tissues for use in structural and functional interactions.

Plasma protein adsorption pattern on characterized ceramic biomaterials

The protein/biomaterial interactions of three biomaterials used in hard tissue surgery were studied in vitro. A dynamic flow system and two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) were used to investigate the adsorption of proteins from diluted human plasma on hydroxyapatite, alumina and zirconia, with regard to total protein binding capacity, relative binding capacity for specific proteins and flow-through and desorption patterns. The ceramics were characterized regarding physicochemical properties; namely, chemical composition by elementary analyses and specific surface, pore volume and pore size distribution using the BET-method and Hg-porosimetry. The materials were found to adsorb a surprisingly low amount of plasma proteins, leaving more than 70% of the surface free. The cellular response will therefore be highly affected by the physico-chemical properties of the material, in contrast to a surface fully covered with proteins. Regarding the adsorption of proteins, most proteins exhibited similar flow-through patterns on the three adsorbents. The exceptions with different flow-through patterns were apolipoprotein D (Apo D), apolipoprotein J (Apo J), complement factor C1s (C1s), complement factor C3 (C3), ceruloplasmin, fibrinogen, alpha1 B glycoprotein and alpha2 HS glycoprotein and serum retinal-binding protein (SRBP). The role of these proteins on acceptance or rejection of implants has to be investigated.

Interaction of glucuronic acid and iduronic acid-rich glycosaminoglycans and their modified forms with hydroxyapatite

Proteoglycans and their spatial arms, glycosaminoglycans (GAGs), are known to interact with hydroxyapatite (HAP) and have been implicated as important modulators of mineralisation. In the present study isotherm data (0.02 M sodium acetate, pH 6.8) revealed that the iduronic-rich GAGs heparan sulphate, heparin and dermatan sulphate showed greater binding onto HAP with higher adsorption maxima compared with the glucuronic acid-rich GAGs chondroitin-4-sulphate, chondroitin-6-sulphate and hyaluronan. Chemically desulphated chondroitin showed no adsorption onto HAP. With the exception of hyaluronan, the GAGs studied showed no desorbability in sodium acetate buffer only, whereas in di-sodium orthophosphate, desorption occurred much more readily. The data indicates that GAG chemistry and conformation in solution greatly influence the interaction of these molecules with HAP. The conformational flexibility of iduronic acid residues may be an important determinant in the strong binding of iduronic acid-rich GAGs to HAP, increasing the possibility of the appended anionic groups matching calcium sites on the HAP surface, compared with more rigid glucuronic acid residues. This work provides important information concerning interfacial adsorption phenomena between the organic-inorganic phases of mineralised systems.

Affinity binding phenomena of DNA onto apatite crystals

The effect of DNA on the crystal growth of hydroxyapatite (HAp) and its morphology was examined. X-ray diffraction patterns of DNA-containing apatites showed typical apatitic features. However, crystal growth was greatly inhibited in the presence of DNA during synthesis; particularly, the crystallinity in the a-axis direction decreased dramatically at low concentrations of DNA. The a- and c-axis dimensions of each precipitate were almost the same, which implies that DNA molecules affect only the crystal surface. CHN analysis clearly showed the presence of these elements, which increased with an increase in DNA concentration in the solution. Scanning electron micrographs of the precipitates formed in the presence of DNA showed typical needle-like crystals, with a decreased crystal size, especially width. Infrared absorption spectroscopy of the DNA-containing apatites showed that the 1630-1700 cm(-1) absorption band due to C=C and C=N stretching increased with an increase in DNA concentration during precipitation. The ESCA spectrum of HAp(DNA 1.0) shows N 1s and C 1s peaks that are absent and weak, respectively in HAp. 31P NMR spectroscopy revealed a weak peak at the base of the 31P peak from the PO4(3-) ions in the HAp crystals. This weak 31P peak had a small positive shift from the position found in native DNA which may be due to the phosphate backbone of adsorbed DNA. The apparent solubility of the HAps increased with an increase in DNA concentration. These results suggest that there is an affinity binding between apatite crystal and DNA molecules.

Effects of exogenous N-acetylhexosaminidase on the structure and mineralization of the post-ecdysial exoskeleton of the blue crab, Callinectes sapidus

A cuticular glycosidase with characteristics of N-acetyl-beta-D-hexosaminidase (HexNAcase) was identified in post-ecdysial crab cuticle. Its appearance coincided with changes in cuticular glycoproteins and the onset of mineralization. To test if HexNAcase might be the causative agent in the alteration of the glycans and initiation of calcification, newly molted crab cuticle was treated with exogenous HexNAcase. Treating cuticular extracts from crabs at 0 h post-ecdysis with exogenous HexNAcase mimicked those changes observed in vivo. Specifically, the enzyme decreased the concanavalin A affinity of an 83-kDa glycoprotein that binds to calcite crystals in vitro. Treating pieces of 0 h post-ecdysial cuticle with HexNAcase rendered them capable of nucleating calcite in vitro (similar to 5 h post-ecdysial cuticle), while untreated, 0 h controls remained uncalcified. The data imply a role of the cuticular HexNAcase-like enzyme in the initiation of calcite nucleation in the newly formed exoskeleton.